In _Megatherium_ the general appearance of the skull is distinctly sloth-like, but the facial portion is more elongated, partly owing to the development of a prenasal bone, and the zygomatic arch is complete. The mandible is very deep in the middle, and is drawn out into a long spout-like process in front. Anteaters (Myrmecophagidae) have a much modified skull, and this is especially the case in the Great Anteater, _Myrmecophaga_. The skull is smooth and evenly-rounded, in these respects recalling that of _Echidna_, but it is longer and tapers much more gradually than in _Echidna_. The occipital condyles are remarkably large. The premaxillae are small, and the long rostrum is chiefly composed of the maxillae and nasals with the mesethmoid and vomer. The zygomatic arch is incomplete, and there is no trace of a separation between the orbit and the temporal fossa. The palate is much elongated, the pterygoids meeting in the middle line just like the palatines. The mandible is very long and slender, there being no definite coronoid process, and a short and slight symphysis. The hyoid arch is noticeable for the length of the anterior cornu. In the Armadillos (Dasypodidae) the skull varies a good deal in shape, but the facial portion is always tapering and depressed. The zygomatic arch is complete. In _Dasypus_ and _Chlamydophorus_ the tympanic bulla is well ossified. In the Glyptodontidae the skull is very short and deep; the zygomatic arch is complete, and has a long downwardly projecting maxillary process. The mandible is massive, and has a very high ascending portion. In the Manidae the skull is smooth and rounded, the zygomatic arch is incomplete, and the orbit is inconspicuous. The palate is long and narrow, but the pterygoids do not take part in its formation. The mandible is slightly developed and has no angle or coronoid process. In _Orycteropus_ the zygomatic arch is complete, and there is a small postorbital process to the frontal. The mandible is well-developed, having a coronoid process and definite ascending portion, and the hyoid is well ossified. SIRENIA. The skull, and especially the brain case of all Sirenia, is remarkable for the general density of the component bones, which, though often very thick, are without air sinuses. It is noticeable also for the roughness of the bones, and the irregular manner in which they are united together. [Illustration FIG. 92. LATERAL VIEW OF THE SKULL OF _Rhytina stelleri_ × 1/8. (Brit. Mus.) 1. frontal. 2. parietal. 3. zygomatic process of the squamosal. 4. squamosal. 5. exoccipital. 6. occipital condyle. 7. pterygoid process of the alisphenoid. 8. jugal. 9. premaxillae. 10. angle of the mandible. 11. maxillae.]